Wind turbines are known from the prior art. They usually comprise a rotor that is rotatably arranged on a nacelle, wherein the nacelle in turn is rotatably arranged on a tower. The rotor drives a generator, possibly via a rotor shaft and a transmission. A wind-induced rotational motion of the rotor can thus be converted into electrical energy, which can then, via inverters and/or transformers—also at least partly directly, depending on the design of the generator—be fed into an electricity grid.
If the energy generation or the infeed of energy is discontinued in a wind turbine, for example because there is a fault in the grid or the wind turbine, or the grid operator makes a corresponding request, the wind turbine is put into idling mode or coasting mode.
If the wind turbine is to be put back into service after the fault that has occurred has been rectified or at the request of the grid operator, the wind conditions at the wind turbine are regularly observed in the prior art over a certain period of time after elimination of the fault or after receipt of the request. A corresponding check over a period of, for example, two minutes is required in order to preclude, solely on the basis of a gust, the assumption of a wind speed sufficient for starting the wind turbine. The latter could be the case, for example, if solely the momentarily measured wind speed were checked for starting the wind turbine. Since each operation of starting a wind turbine can represent a significant load for individual components of the wind turbine, it is ensured, by observation of the wind conditions over a certain time period before the actual starting up of the rotor of the wind turbine, that the wind turbine will not unsuccessfully attempt to start due to a gust.
A disadvantage of this prior art is that after elimination of a fault of the wind turbine or the grid, or after receipt of a request from the network operator, a certain period of time, for example of two minutes or more, passes before the wind turbine is actually started up to feed to electrical energy into the grid.